Syria has the potential to become America’s new Vietnam — so, as Barack Obama sends the first 50 special operations troops to Syria to engage the Islamic State, we must be wary of history repeating itself.

The original mistake with Syria, as with Vietnam, was for leaders in Washington to believe that civil wars and insurgencies taking place halfway around the world represent a critical national security interest. Back then, the illusory “domino theory” — the idea that if one nation went communist it would start a chain reaction leading all the other nations in the region to do the same — justified the decision to engage in a tiny nation that itself represented zero threat to the United States. A version of that logic is at work again.

We’ve been told that it matters a great deal to US security interests whether Assad rules in Syria — but it does not. At last check an Assad has run Syria since 1970 without requiring US intervention. And any successor regime inheriting a destroyed Syria could hardly be a threat. Nonetheless, this assumption creates a powerful bias toward intervention that is difficult to check regardless of the strategic reality.

Before that original “forever war”, President John F Kennedy also told Americans that the United States was only training the South Vietnamese army. But US engagement eventually metastasized into a full-blown military intervention.

Today, after unnecessarily intervening in Syria, the US made things worse by embracing ineffectual and costly relationships with local partners on the ground. After years of arguing that there were no Syrian rebels worth supporting, the Obama administration then decided to try anyway and proceeded to waste hundreds of millions of dollars on perhaps the least successful training effort in US history. As the Centcom commander testified, only “four or five” trained rebels are in the fight.

It’s mystifying why Obama would commit such a colossal mistake when Vietnam provided so many painful lessons in avoiding precisely this kind of situation.

After the fall of Dien Bien Phu in 1954, the Eisenhower administration decided to begin supporting South Vietnam directly. The first casualties of US advisers in Vietnam occurred in 1959. The following year, nearly 700 advisors were operating in Vietnam, with Kennedy tripling the numbers the following year. By 1968, more than 500,000 US service members were in Vietnam.

Vietnam showed that the failure of an initial limited intervention creates political pressures for more aggressive action. In theory, a president should be willing to pull the plug if the initial failure makes clear that intervention is a bad idea. Most often, however, once a president has intervened, his political status is now yoked to the policy; pulling out risks almost certain censure for “losing”.

Regardless of whether things are going poorly, therefore, presidents face tremendous pressure to throw good money after bad. As declassified records later revealed, Lyndon Johnson realized early on that he would not achieve victory in Vietnam. He continued the war, however, in order to preserve the political capital he needed to push ahead with his Great Society programs.

And both the 2007 and 2010 surges in Afghanistan and Iraq are powerful examples of exactly this same kind of reasoning. Neither Bush nor Obama wanted to face the political fallout of withdrawal and perceived failure.

Having promised the world that he would “degrade and ultimately destroy” Isis, Obama now finds himself continually pressed to take more aggressive actions in the Middle East, despite his own doubts about their effectiveness. Most recently, for example, Obama admitted that he had approved the training program for the Syrian rebels even though he never thought it was likely to work.

US military power cannot compel democracy in foreign lands; neither can it force change amongst foreign populations. Only those governments and their people can effect political change if they themselves want it. That is just one of the many lessons that Vietnam can teach the current administration — if, that is, they are willing to learn.